1. Field of the Invention
The present invention relates to a digital demodulating apparatus, a digital receiver, a controlling method of the apparatus, a computer program product, and a recording medium recording thereon the product.
2. Description of Related Art
In a digital demodulating apparatus that applies channel select processing and demodulation processing to a received signal, the signal to be demodulated may contain a noise component to a desired component. A large affect of the noise component encumbers the accurate demodulation. Therefore, the affect of the noise component is preferably small to the desired component.
Japanese Patent Unexamined Publication No. 2001-526485 discloses a receiver that measures a nonlinear component contained in an output signal from a demodulator to perform bias control of each amplifying stage on the basis of the measurement result. The nonlinear component is generated due to the nonlinearity of each circuit element, and it is one cause of a noise component contained in a signal to be input to the demodulator. In the above Publication, the receiver measures the quantity of the nonlinear component contained in a signal from the demodulator, and controls the 3rd order input intercept point (IIP3) of each circuit element in accordance with the measurement result. The linear performance of the receiver is thereby controlled. Thus, the noise component is suppressed that is caused by the nonlinear component contained in the signal from the demodulator.
On the other hand, even when the linear performance of each circuit element is ensured to a certain degree, the demodulation may not accurately be performed. For example, when the receiver receives a large interference, the signal is distorted unless the gain of each amplifying stage is properly controlled. In the above Publication, however, an AGC control circuit controls the gain of each amplifying stage independently of the measurement result of the nonlinear component. Thus, a proper gain control may not be performed in each circuit element such that the distortion of the output signal is suppressed.